This blog is the final product of my dedicated research on the controversial Mullaperiyar Dam since 2006. This dam constructed in 1895, in lime surkhi mortar when dam engineering was at infancy, now hangs like a Damocles Sword over the lives and properties of millions of people in the Central Kerala region. Please be united to avert the doomsday!

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Saturday, November 26, 2011

Mullaperiyar Dam - Technical Details

River Periyar originates from the Western Ghats in ‘Sundara Malai’ in the Sivagiri group of hills at an elevation of about 1830m above MSL. From its origin, it traverses through an immense cliff of rocks in a northerly direction receiving several rivulets in its course. About 48 Km downstream, the Mullayar joins the main River at an elevation of 845m above MSL and the River then flows westwards. About 11 Km downstream of the above confluence, the river passes through a narrow gorge. A dam was constructed at this gorge to intercept the flow and it got christened as ‘Mullaperiyar dam’, which received the above title from the rivers Mullayar and Periyar. The dam have a catchment area of 624 square kilometres, which lies completely inside Kerala territory.

The Mullaperiyar dam is having a length of 1200 feet and a height of 155 feet from the river bed and the height from the deepest foundation is 176ft. The front and rear faces of the dam are of uncoursed rubble masonry in lime, surki and sand mortar. The hearting is of lime surkhi concrete with 3.125 parts of stone and 1 part of mortar. The proportion of lime surkhi mortar is 2 parts of lime, 1 part of surkhi and 3 parts of sand.The central core constructed with lime surkhi concrete occupies about 60% of the total volume of the dam. As part of the strengthening measures suggested an RCC capping was added to the top of the dam. Also a 10 m concrete backing was provided to the downstream side, but the joint between the old dam and the new dam remain ungrouted even though shear keys were provided.

The main dam is having two saddles on the left and right banks. The left bank saddle of 483 feet length was closed by means of a masonry dam named ‘baby dam’ of length 240 feet and height of 47 feet and the remaining portion by an ‘earthen bund’. The baby dam is also designed as a solid gravity dam constructed in similar fashion as the main dam. The right bank saddle is converted as a surplus arrangement by providing 10 vents of 36ftx10ft and 3 additional new vents with 40ftx10ft with a crest level of 136 feet.

The Mullaperiyar reservoir was conceived in 1886 with an FRL of 144ft (Please See 'History of Periyar Project by A.T. Mackenzie, 1899). But in 1908 after 13 years after completion of the project, the FRL was raised from 144ft to 152ft without the concurrence of Travancore. This FRL was reduced to 150ft in 1964 and then to 145 ft in 1978 and further to 136ft in 1979 due to safety concerns. The gross and live storages of the Mullaperiyar reservoir at various levels are given below for a quick glance:

Full Reservoir Level in feet

Gross Storage in TMC

Live Storage in TMC

136

11.210

6.118

142

12.758

7.666

144

13.299

8.207

152

15.662

10.570

The average inflow data for the last 50 years (1960-2009) shows that 23.5 TMC while the 50% dependable flow is 22.2 TMC. While the 75% and 90% dependable inflows for the same period is 18.5 TMC and 14.1 TMC respectively (1 TMC, ie, Thousand Million Cubic Feet = 28.317 Million Cubic Meter). [Source: Tamil Nadu Public Works Department Records]

The diversion data shows that Tamil Nadu had diverted 20.67 TMC on an average basis (1963-2010) and the 75% dependable diversion for the same period was 17.76 TMC. (Source: Tamil Nadu Public Works Department Records)

The water from the Periyar Lake is taken through an open cutting having a length of 5342 ft and a bed width of 21 ft. Then the water is controlled through a tunnel, which is regulated by a head sluice at the entry of tunnel. The tunnel is of height 12ft and length of 5887 ft with a sectional area of 150 sq. ft and is now capable of discharging 2100 cusecs. But normal operation conditions only 1600 cusecs are drawn through this tunnel.

Then the water is collected after at a fore bay dam of capacity of just 3.2 Mcft and from there water is taken through a power tunnel of length 3992 feet with a discharge capacity of 1600 cusecs. This forebay dam is also provided with an irrigation sluice to discharge waters exclusively to Cumbum Valley. The power tunnel terminates at a surge shaft and from there the water is taken through 4 penstock pipes each with a discharge capacity of 400 cusecs to the Lower Camp Power House (4x35 MW) which generates 500 Million Units (MU) of electricity annually.

After power generation, the tail waters are discharged into Vairavanar, a tributary of the Suriliyar River, which is a tributary of Vaigai River. The tailwaters thus released are then collected at the Vaigai Reservoir and then released for irrigation purpose. The gross command area envisaged for the Project is 90,000 acres for the first crop and 60,000 acres for the second crop (Ref – History of Periyar Project, A.T. Mackenzie, 1898).

Thank you for posting interesting technical and legal aspects of the Mullaperiyar issue and for being a sane voice trying to explain the scientific and legal aspects of this problem in the midst all the attempts to inflame passion. Could you comment on the following aspects of this issue

1) Why did Central Water commission attempt to lower the height of water in 1979? Was the possibility of a new dam discussed at this point? What were the measures taken to supposedly strengthen the current dam and were they effective?

2) what is the purpose and effectiveness of the "baby dam"?

3) Several questions are being raised as to the earthquake resistance capability of the idukki dam(s) as well. Could you comment on its constructional aspects and earthquake resistance as well in light of the improved knowledge of seismic activity in the area?

All river water and dams needs to be nationalised otherwise these petty disputes will endanger people and their very livelihood. This is more so with number of states getting divided left right and centre.

The central government with the guidance of Supreme Court, must see to that Technical committee is set up comprising of neutral Technical people along with one each from both the states. The technicality of the issue should be studied thoroughly including that of earthquake factor. Te matter must be resolved amicably and not by force.

One more thing how many tremors were there actually in the Mullaiperiyar dam region actually?Were there earthquakes or tremors?What was the intensity?How many of them were reported by the media?How many were actually reported by the siesmological department?How safe is the Idukki dam which will cause more devastation than Mullaiperiyar dam?

Your dam and your water then why you people are coming to tamilnadu for your surviving. All over the world only in Tamil Nadu most of the malayali's are settled & keep on migrating. I am asking to the Kerala government - please raise a statement that "call all malayaali's who settled in tamil nadu to their own state kerala".If malayaali's moved out Or wiped out from tamilnadu, TN Population will decrease like anything. But think about kerala....already population density is high...if people are permanently moved out to kerala from TN, how you people can survive over there. My humble request Please always keep it mind "Kerala is is not a Country , Also it is a state in INDIA". So follow the government rule. don't put yourself in trouble, always don't think who ever in kerala are the only malayali's people. Please always remember more than 30 lakhs malayali's in tamilnadu.

Your dam and your water then why you people are coming to tamilnadu for your surviving. All over the world only in Tamil Nadu most of the malayali's are settled & keep on migrating. I am asking to the Kerala government - please raise a statement that "call all malayaali's who settled in tamil nadu to their own state kerala".If malayaali's moved out Or wiped out from tamilnadu, TN Population will decrease like anything. But think about kerala....already population density is high...if people are permanently moved out to kerala from TN, how you people can survive over there. My humble request Please always keep it mind "Kerala is is not a Country , Also it is a state in INDIA". So follow the government rule. don't put yourself in trouble, always don't think who ever in kerala are the only malayali's people. Please always remember more than 30 lakhs malayali's in tamilnadu.

Thank you for the info. Could you please give a better idea of the spillway ? If you calculate the capacity as per the dimensions given, the capcity would be much lower than what is mentioned every where.

From google earth I could see that 40 and 36 are width of the spillway and 10ft being the height. I have done the calculations for an open channel (which has the highest flowrate among all, 3.367*b*h(3/2))).Qmax (40ft/10ft) = 6695.17 cusecs. Qmax (36ft/10ft) = 6025.65 cusecs. Total - 6695.17 x 3 + 6025.65 x 10 = 80342 cusecs

Thanks,VarkeyAlso, since the effective head loss is lower due to the steppings below (dissipater), the effective volume should be much lower than the above calculation. Also the spill way is not regulated I suppose. I believe the spillway capacity is overstated. That is tamilmatics.

Solving the Horizontal acceleration equation given on page 13 of the IITR report gives 'a' as 0.091 and not 0.16 as given in the report. can any one explain the error? Or is it a delibrate error by IIT professor? The Mathematica code for solving the equation is given below so you too can tryM = 6.5;r = 16;F = 1;e = 1;Solve[Log[a] == -0.62 + 0.177 M - 0.982 Log[r + E^(0.284 M)] + 0.132 F - 0.0008 e, a]

If Dam collapse keralites losses life, Tamil losses water, By reducing water reservior Tamil losses water, Keralites should remain in fever. So better to construct a new dam that good for both.Actually these tamils are not thinking that if kerala is not giving water then where will go this water, kerala cannot afford these much of water in a dam or in the whole state.

Tamil People and Kerasla need not quarrel due to suspicions on the New Dam which is almost identical as the old dam in respect of FRL and MWL.So Tamils get their water.But since they arde in doubt and since Union Governmenbt is erroneously supporting on Dam safety,Tamils cannot be blamed to lurk under fears.The culprit is the Union Government and their pseudo experts who are misleading Tamilnadu.Today,Kerala has a duty to save 35 lakhs of people from getting drowned due to damfailurde for one reason or the other as 40 dams failed in India also and this dam is under-designed for seismicity and hydrology and Environmentzal aspectshttp://tshivajirao.blogspot.com/2012/01/under-designed-dams-collapsedhydrologic.htmlhttp://bhujangam.blogspot.com/2012/01/mullaperiyar-dam-will-burst-due-to.html.So,kerala must build two or three smaller dams only to absorb the Dam Break floods.Kerala must call for international tenders inviting bids to study the problem and suggest where such smaller Dams can be built to save the keralites from an impending Disaaster waiting in the wings and this work does not need the consent of Tamilnadu as kerala is building its Dams in its own territory.Work should be done immediately because a stitch in time saves nine. Prof.T.Shivaji Rao,Director,Cdentre for Environmental studies,Gitam Univdersity,visakhapatnam

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About Me

Assistant Executive Engineer (Civil), Kerala State Electricity Board. Specialised in the inter state water disputes.
Presently working as a member of the Mullaperiyar Special Cell, Government of Kerala on deputation. Associated with Mullaperiyar case since 2006.